1. Field of the Invention
The present invention relates to a system and method for assembling an internal combustion engine and further relates to a system and method for correlating engine information with a vehicle identification number.
2. Description of Related Art
During assembly of an internal combustion engine, a piston is inserted into each cylinder formed in an engine block. The cylinder must have an inner diameter that is slightly larger than the outer diameter of the piston in order to provide a desired piston clearance. The piston clearance is the distance from the outer surface of the piston to the opposing inner surface of the cylinder.
Engine blocks are typically die-cast and machined to form cylinders having an inner diameter that is within a predetermined cylinder inner diameter tolerance, meaning that the specific diameter of each cylinder is measured and confirmed to be within a range of acceptable cylinder inner diameters, which is defined as the desired inner diameter plus or minus an acceptable variation. The lowest cylinder inner diameter tolerance limits that are considered technological feasible using current manufacturing processes are about ±10 μm. Conventionally, once the inner diameter of each cylinder is confirmed to be within the cylinder inner diameter tolerance, the engine block is passed for further assembly.
Similarly, pistons are conventionally cast and then machined to have an outer diameter that is within a predetermined piston outer diameter tolerance, meaning that the specific outer diameter of the piston is measured and confirmed to be within a range of acceptable piston outer diameters, which is defined as the desired outer diameter plus or minus an acceptable variation. The lowest tolerance limits of the piston outer diameters that are considered technological feasible using current manufacturing processes are about ±10 μm. Once a piston is confirmed to be within the piston outer diameter tolerance, the piston is deemed acceptable for use in the assembly of an internal combustion engine.
At an appropriate point along the assembly line in the conventional method of internal combustion engine assembly, pistons that have previously been determined to be within acceptable piston outer diameter tolerance limits are inserted into cylinders that have previously been determined to be within acceptable cylinder inner diameter tolerance limits. Since each of the pistons and cylinders are within predetermined limits, the resulting piston clearance, although unknown, will necessarily be within the predetermined range of acceptable piston clearance. The engine block, with the pistons inserted into the cylinders, continues along the assembly line for further assembly of various engine components and, thereafter, is installed in a vehicle.
Although the conventional method of assembling internal combustion engines has been used for many years to produce high quality engines, a very small percentage of internal combustion engines produced in accordance with the conventional method exhibit engine-related problems such as, for example, lack of power, unacceptable engine noise, seizure and hard running. Examination of disassembled problem engines suggests that many of these engine-related problems can be attributed to inadequate or excessive piston clearance in one or more cylinders.
It is believed that when a piston that is at the extreme low end of the acceptable piston outer diameter tolerance limits (i.e., the specific outer piston diameter of the piston is about equal to the desired outer piston diameter minus the acceptable variation) is inserted into a cylinder that is at the extreme high end of the acceptable cylinder inner diameter tolerance limits (i.e., the specific inner diameter of the cylinder is about equal to the desired inner cylinder diameter plus the acceptable variation), the piston clearance will be greater than desired. This can produce a “loose” engine, which may suffer from a lack of power or produce unacceptable engine noise. Conversely, when a piston that is at the extreme high end of the acceptable piston outer diameter tolerance limits (i.e., the specific outer piston diameter of the piston is about equal to the desired outer piston diameter plus the acceptable variation) is inserted into a cylinder that is at the extreme low end of the acceptable cylinder inner diameter tolerance limits (i.e., the specific inner diameter of the cylinder is about equal to the desired inner cylinder diameter minus the acceptable variation), the piston clearance will be less than desired. This can produce a “tight” engine, which may be hard running, noisy, or may ultimately seize. The ambient/environmental conditions in which the engine is frequently operated (e.g., predominantly cold geographic regions, predominantly hot geographic regions, high altitudes) as well as maintenance and driving conditions may also exacerbate such potential engine-related problems.
As will be appreciated, such engine-related problems are infrequent. The vast majority of internal combustion engines produced in accordance with the conventional assembly method do not have piston clearances that are problematically greater or less than desired. As noted, in order for piston clearance engine-related problems to arise from the conventional engine assembly method, it is believed that a piston having a specific outer diameter that is at or near the extreme upper end or lower end of the acceptable piston outer diameter tolerance limit must be inserted into a cylinder having a specific inner diameter that is at or near the extreme lower end or upper end, respectively, of the acceptable cylinder inner diameter tolerance limit. Moreover, it is believed that several of such piston/cylinder combinations must exist within an engine, and that the engine must be operated in a harsh environment, before such piston clearance engine-related problems are experienced.
In addition to being uncommon, it is difficult to diagnose a piston clearance related problem in an engine once it has left the manufacturer. Because the specific piston outer diameters and specific cylinder inner diameters are not recorded and associated with the host vehicle, it is impossible under the present engine assembly method to determine if piston clearance may be problematic without tearing down the engine and inspecting the components. Vehicle owners are understandably reluctant to allow a manufacturer to have possession of their vehicle for extended periods of time and to permit the manufacturer to tear down the engine and examine its various components. Moreover, in “tight” engines in particular, increased friction may cause the pistons and/or cylinders to wear and/or the engine to seize; a determination with certainty of the cause of the engine problem is nearly impossible in a worn or seized engine.
Thus, there exists a need in the art for a system and method for assembling an internal combustion engine wherein the actual measurements of the pistons and cylinders are used to select a particular piston for each cylinder, and wherein the resulting piston clearance is within a predetermined piston clearance tolerance. Moreover, there exists a need in the art for a system and method for correlating engine information with the host vehicle so as to permit retrieval of such engine information should an engine-related problem be reported.